Interpolyamide



Patented June 2, 1942 IN TERPOLYAMIDE Merlin Martin Brubaker, William E. Haniord, and Richard H. Wiley, Wilmington, Del., assignors to E. I. du Pont de Nemours & Company. Wilmington, Del., a corporation of Delaware N Drawing. Application February 24, 1941, Serial No. 380,366

8 Claims.

This invention relates to synthetic polymeric materials and more particularly to synthetic linear interpolyamides.

, In Carothers Patents Nos. 2,252,554, filed September 19, 1938, and 2,252,555, filed April 4, 1939, both of which applications have been assigned to the assignee hereof, reference is made to Carothers Patents 2,071,250, 2,071,253, and 2,130,948, which particularly describe polyamides derived from the reaction of a single diamine with a single dibasic carboxylic acid or from the polymerization of a single amino acid. The said applications contain disclosures of further polyamides, namely, interpolyamides formed respectively from four or more retactants consisting of diamines and dibasic carboxylic acids, or from three or more reactants consisting of an amino acid, a diamine, and a dicarboxylic acid. As

brought out in the said applications, both of these latter subgenera of polyamides possess characteristics which differ substantially from certain of the characteristics of the simple polyamides revealed in the aforesaid patents. For a number of industrial uses, however, a demand has arisen for varieties of polyamides differing still more widely from the said simple polyamides and possessing, e. g., greater pliability. Frequently, also, greatly enhanced solubility characteristics are needed, along with the increased pliability, and as a rule it is important that relatively high melting or softening points nevertheless be preserved. This last-mentioned objective has proven very difllcult of fulfillment since ordinarily increased pliability and increased solubility of the polyamides go hand in hand with decreased melting point.

This invention has as an object the prepara tion of polyamides satisfying the aforesaid demand. This invention has as a further object the production of interpolyamides having appropriate pliability, solubility, and melting point characteristics for fabrication into wrapping foils or for use in coating fabrics or other structures that customarily are subjected to a great deal of flexing during use, or that also are customarily subjected to heat treatments during use, e. g. in laundering or calendering.

The foregoing objects, as well as others which will appear either expressly or impliedly hereinbelow, are accomplished by inter-polymerizing, in

the manner and proportions more fully described hereinbelow, at least three polyamide-forming compositions, i. e., compositions which are per se capable of forming a linear polyamide, the said compositions being selected from the class consisting of B-aminocaproic acid, hexamethylenediamine-adipic acid salt, hexamethylenediaminesebacic acid salt, and the hereinbelow referred to mixed salt of hexamethylenediamine with suberic and azelaic acidsidesignated, for convenience, as hexamethylenediammonium azelatesuberate). It should be understood that reference to fi-aminocaproic acid in the specification and appended claims includes also the equivalent amide-forming derivatives thereof, e. g., the esters, lactam, acid halides, N-formyl derivative and, when water is present or developed in the polymerization reaction, G-aminocapronitrile. Similarly, reference to the diaminedibasic acid salts includes also amide-forming derivatives of the corresponding diamine and dibasic acids. As amide-forming derivatives of the diamine might be mentioned the carbamate and the N- formyl and N,N'-diformyl derivatives. Amideforming derivatives of the dibasic acids include the monoesters, diesters, anhydrides, amides, acid halides, and when water is present or developed in the polymerization reaction, the mononitrile or dinitrile.

The mixed salt (hexamethylenediammonium azelate-suberate) referred to aboveis that obtained from hexamethylenediamine and a mixture of suberic acid and azelaic acid in which the acids are present in proportions corresponding to the suberic acid-azelaic acid ratio produced by the oxidation of oleic acid, e. g., with chromic or nitric acid. This ratio is generally within the range 15:85% to 30:70%.

It is essential to the securing of the desired balance between preservation of the most desirable characteristics of solubility, pliability and melting point, and sacrifice of the said three properties or any of them, that none of the hereinabove specified per se polyamide-forming compositions be present in the initial reacting system to an extent greater than nor, in the case of at least three of them, to an extent less than 5%.

Furthermore, since the unique utility characteristic of the new class of interpolymers rests broadly on the achievement of unusually high melting point and solubility characteristics without undue sacrifice of pliability, and since it now has been foimd that for certain fields of use, e. g., coated fabrics, artificial leather and wrapping film, the employment of interpolymers having a modulus of stiffness less than that presently to be specified is critically necessary, mathematicsl tests, also presently to be specified, have been developed from data obtained during the course of exhaustive research on the subject, as guides for use in the practice of the invention. It is powble, by resort to these mathematical tests, to determine in advance whether or not the proportions in which the three or more hereinabovc-speciiled per se polyamlde-forming coun-v positions are reacted will yield produets having a modulus of stiffness below the aforesaid figure, or, as well. the hereinafter specified degree of solubility in aqueous alcohol, which is an useful solvent medium for the new interpolymers.

The aforesaid modulus of stiffness (also referred to as bending modulus) below which the pliability of the interpolymers need to be maintained, for the aforesaid special uses, is 50x10 lbs./sq. in., as measured on the hereinafteridentified Tinius-Olson stiffness tester.

The hereinabove referred to degree of solubility in aqueous alcohol, of special importance when the new interpolymers are to be applied, or formed into the desired articles, from solution rather than from melt, is at least 15% in hot (50-75 C.) 80% aqueous ethyl alcohol. This degree of solubility makes possible the successful formation of the new interpolymers into films, sheets, coatings, or the like from solution, without incurring the disadvantages which accompany the use of corrosive, highly toxic solvents such as have been necessary in effecting application of thesimpler polyamides from solution.

Where the polymers are to be used in applications involving exposure to elevated temperatures, e. g. boiling water or steam, it is desirable that those species be employed which have melting points of 140 C. or higher.

The hereinabove mentioned mathematical tests for selecting varieties of the new interpolymers having a modulus of stiffness such as above referred to, i. e. of less than 50x10 lbs/sq. in., consist in the following two equations.

(1) X+Y+Z+r=100 X=l-0.333T+ [0.02--(T-l5) [2-29- wherein X stands for minimum percent composition of epsilon-aminocaproic acid, and does not exceed a maximum of 85, Y stands for percent composition of hexamethylenediammonium sebacate, Z stands for percent composition of hexamethylenediammonium adipate, and T stands for the percent composition of mixture of hexamethylenediammonium salts derived by the reaction of hexamethylenediamine with the aforesaid mixed oxidation product of oleic acid, or with a suberic acid-azelaic acid mixture in the aforesaid proportions, corresponding to the said oxidation product; the values for x, Y, Z. and T being positive and not more than one ofv them equalling zero.

aseaooe ihesolutionofthisequationgivestheminimum The value of Y may be obtained by substituting these values in Equation 1. The following table illustrates the results of such procedure where an initial valueof 15isto Tandthe calculations are carried out for values of Z ranging from 0 to '10.; The "2:" column contains the minimum values of x obtained from Equation 2, and the "Y" column contains the corresponding maximum values of Y. For example, in the first row of this table T=l5, 2:0, and any value of x may be chosen in the range 23.4 to 85%, while Y may vary from 81.8 to 0%.

new 1 'r z x v is 0 2.4 61.0 16 10 13. 26 61. 7 is 20 1.12 51. a is so a 1 so 15 w 1210 22a is an 220 2.4 15 10 are It will be noted that a value of 70 for Z, when T equals 15, does not satisfy Equation 1 with positive values since the sum of T, Z, and X is greater than 100. Therefore, Equation 1 cannot be satisfied with positive values of Y, and it thus becomes apparent in advance that interpolyamides formed with T equal to 15 and Z equal to 70 will possess a modulus of stiflness greater than 50x10 lbs/sq. in.

The hereinabove-mentioned mathematical test for selecting varieties of the new interpolymers which not only fulfill the aforesaid modulus of stiffness requirement but also meet the hereinabove described requirement of solubility (to the extent of at least 15% in hot (50-75" C.) aqueous ethyl alcohol) consists in the replacement of Equation 2, in the foregoing test, by the following equation:

X=4+0.0073(T45) -|-0.0322[Y- 13-03043 (I -53) Whether Equation 3 or Equation 2 be employed, in conjunction with Equation 1, it is to be borne in mind that in all cases the value of x represents the minimum value, the value of X may vary from this minimum value upto 85, and that the values of X, Y, Z, and T must each be positive, except that one of them, but only one, may be equal to zero.

It maybe observed that irrespective of the proportions of the respective starting ingredients, the interpolymers formed in accordance with the invention yield, on hydrolysis with mineral acids, monomeric amide-forming reactants corresponding to those from which the respective initial per se polyamide-forming constituents of the said interpolymers were derived.

The following examples, serving to illustrate in detail the practice of the invention, will deal with the preparation of preferred species of interpolyamides which satisfy the said mathematical tests. The particular methods of conducting the polymerization reaction are similar to those set forth in the hereinabove cited patents and applications. The polymerization reaction preferably is carried out-between 200 and 300 C.,and is continued until a polymer of good strength is obtained. For most purposes this means that the reaction is continued until the polymer can be formed with pliable filaments or has an intrinsic viscosity at least 0.4. In the examples, quantities are specified as parts by weight unless otherwise indicated.

' Exurrns I Interpolyamide formed lrom hezamethylenediammonium adipate, hezamcthvlenediammonium sebacate, and caprolactam r In an aluminum liner autoclave are placed 270 parts of hexamethylenediammonium adlpate (the salt of hexamethylenediamine and adipic acid), 202 parts of hexamethylenediammonium sebacate, 202 parts of caprolactam, and 50 parts oi distilled water. The liner is placed in an autoclave under an inert atmosphere and heated at 230 C. and 250 pounds pressure for 3 hours. At the end 01 this time the pressure is reduced over a period of one-half an hour to atmospheric pressure and the autoclave is then evacuated by means 01' a vacuum pump. The heating is continued under a vacuum of 4-10 mm. for three hours at 260-300" C. After cooling under an inert atmosphere and removing from the liner a tough white polymer of intrinsic viscosity 1.97, as defined in U. 8. Patent 2,130,948, and softening point 160-162 C. is obtained. This interpolyamide has a modulus of stillness of 32x l0 lbs/sq. in., as determined on the Tinius-Olsen stiffness tester, and is soluble to the extent of 15% by weight in 80% aqueous ethyl alcohol (80 parts by volume of ethanol and 20 parts by volume of water) to give a solution which is stable at room temperature ior'one hour and fifteen minutes. Other solvents for the polymer are methanol-chloroform mixtures (65:35), ethanoltoluene mixtures (70:30), benzyl alcohol and unsaturated alcohols, e. g., methallyl alcohol.

On hydrolysis with hydrochloric acid the polymer yields fi-aminocaproic acid hydrochloride, hexamethylenediamine hydrochloride, and adipic acid.

EXAMPLE II Interpolyamide formed from hezamethulenediammonium adipate, hexamethylenediammonium salts of oleic acid oxidation acids, and aminocaproic acid Y Twelve parts of hexamethylenediammonium adipate, 10.5 parts of hexamethylenediammonium salts of oleic acid oxidation acids- (2025% suberic and 75-80% azelaic), and 7.5 parts of S-aminocaproic acid are placed in a-glass tube, sealed and heated at 2l0-220 C. for 2 hours. The tube after cooling and opening is heated at 255 C. for 2 hours under a vacuum of 3-4 mm. The

' resulting polymer obtained after the final heating period is a clear white tough polymer having a softening point of 160 C. and a modulus of stiffness of 34x lbs/sq. in., as determined on the Tinius-Olsen stiffness tester. The polymer is soluble to the extent of by weight in 80% aqueous ethyl alcohol and stable without gelling at room temperature for 3.5 hours. I

EXAMPLE III sebacate, and

II, an interpolyamide is prepared irom 9.0 parts of hexamethylenediammonium salts of oleic acid oxidation acids 00-25% suberic and 75-80% azelaic) 7.5 parts of hexamethylenediammonium sebacate, and 13.5 parts or 6-amiaocaproic acid. The interpolymer which is obtained is white. tough, and viscous, has a softening point at 141 C. and is soluble to the extent of 15% by weight in 80% aqueous ethyl alcohol'to live a solution which does not gel alter standing at room temperature for 2.25 hours. It has a modulus of stillness of 38x10 lbs/sq. in., as determined on the Tinius-Olsen stillness tester.

ExassruIV interpolymer formed from hexamethuleaediammonium adipate, hezamethvlenediammonium salts of oleic acid oxidation adds. hezamcflwlenediammonium sebacate, and caprolactam tening point of 149 C. The polymer is 'soluble to the extent or 15% by weight in 80% aqueous ethyl alcohol giving a solution which does not gel until it has stood at room temperature for 2-3 hours. The polymer has a modulus of stiflness of 19x10 lbs./sq. in., as determined on the 'Ilnius-Olsen stiffness tester.

Exmrtr V Interpoluamide formed from hexamethylenediammonium adipate, hemamethylenediammonium salts-of oleic acid oxidation acids, and

' heramethulenediammo'nium sebacate In a manner similar to that described in Example 11, 7.5 parts of hexamethylenediammonium adipate, 18.0 parts oi hexamethylenediammonium salts of oleic acid oxidation acids (20-25% suberic and -80% azelaic), and 4.5 parts of hexamethylenediammonium sebacate are placed in a lass tube and heated first sealed at 210 C. for 2 hours and then under vacuum for an additional two hours. The polymer which is obtained is a white, tough product, has a softening point of 149 C., and is soluble to the extent of 15% by weight in hot aqueous ethyl alcohol, but

gels immediately on cooling. The polymer also is soluble in aqueous ethyl alcohol, in a 70:30 chloroform-methanol mixture, in a 50:50 ethanol-toluene mixture, and has a modulus of stiffness of 38x10 lbs/sq. in., as determined in the Tinlus-0lsen stiffness tester.

As hereinabove indicated, a relatively high melting point is advantageous in most instances, although there are particular applications-tor example, where readily fusible adhesives are required'for which a relatively low melting point may be desired in conjunction, e. g., with a high degree of pliability. In order to facilitate ready selection of preferred interpolyamides o! the invention having melting or softening points suitable for the particular use contemplated, and in order also to facilitate the making or such selection without the necessity oi resorting to the 4 hereinabove-described mathematical tests, the following table is included herein:

the deflection or reading of the pendulum on a calibrated scale when the film has been bent TABLE II Percent composition H th 1 u Modulus o! Sol bill exams y eneu Eenmethylenediamrnonium Hexamethylene- 212:? point stifinen I (gel ting diammonium salts oi oleio diammonium a a in 0.

adipate acid oxidation oebaoats &3

acids 10 45 45 145 8 l 40 30 80 150 51. l. 55 30 175 N 0.5 40 40 145 81. l 45 80 1M 55 2. 5 4 50 10 40 1Q 85. 0 5. 0 25 45 140 55.0 15 101 52.8 0. 5 40 15 45 1M 8! 35 35 155 2B. 1 10. 0 40 35 25 150 88. I 8. 5 25 15 149 48. i 0. 1 20 15 144 85. 5 0.05 15 25 00 143 I 15.

- 30 40 30 138 59. 1 0. l .a. 45 10 a 45 140 Q. 7 00 25 15 153 40. 5 0. 1 e0 15 15 10 34 0. 5 25 45 20 10 148 8). 5 0. 25 15 50 l5 i0 150 80. 5 0. 15 40 15 25 an 154 5 0. 5 40 30 10 20 150 28.0 1.0 30 45 5 I) 140 i 19. 4 48 1 Determined by film-on-block method. Determined by Tinlus-Olsen stifiness tes standing at room temperature.

Dash indicates that gelation had not occurred alter 24 hours.

For a detailed description of the 'Iinius-Olsen stillness tester referred to hereinabove, reference may be had to Bulletin No. 11, Tinius-Olsen Testing Machine Co., Philadelphia. especially Plate 933. The general mode of operation of the said stifiness tester is as. follows:

The strip of film 1" wide is clamped in a rotating vice and at V4" span pushed against a lever arm attached to a weighted pendulum. The measurement gives the force as inch pounds to bend the strip any given angle up to 90. It has been found that any kind of film so far tested gives the same character of curve when force is plotted against angle. The line is straight from the origin up to 40 or 50 angle, but then curves away from theforce coordinate. On reversal of the rotation the original lineiis not retracted, due to a bend left in the film. The residual bend 30'. This reading on the scale multiplied by the weight placed on the pendulum gives the force in gnach pounds required to bend the him through A sample calculation, for the polymer formed by the interpolymerizationof 40 parts of hexamethylenediammonium adipate, 30 parts of her:- amethylenediammonium sebacate and 30 parts of G-aminocaproic acid-which polymer constitutes oneof the especially preferred products of the invention, by reason of its unusually valuable combination of high degrees of pliability and solubility together with relatively high melting point-follows:

The thichiess'of the film was 0.0200 inch an at a 80' bend using 0.155 pound-weight, the dem fiectionwas'll'fi. That is:

is not necessarily permanent but is always the 33 3 same. If the bend is stopped at 30, however, the 7 1 original line is much more nearly retraced and jg the residual bend hardly ever exceeds 3'. In 55 practice it is found that repetitional bends to 30 Substituting:

at the same spot on the film may be made five W 01' six times. at least, duplicating the force each 0.5 5 J) time, by adjusting the contact between trials for M- the residual bends.

The method of operation adopted for the tests set forth herein accordingly has been to meas- 5X0 71 ure the force for 30 angle bends. In the theo- 75(= retieal modulus (developed fromXotmg's modu- (o 6 lus) which has been worked out and employed 5 which an for determining the moduli of stifiness set out or referred to herein, the final equation is 0.575(0.440)

a being the thickness of the one inch piece of film. W the weight in pounds. g the percent defiection at 30 bend and s, the span, equal to or 0.0316X10' lbsJsq. 1a., or 31.6)(10 lbsJsq. in. While It measures the intrinsic stillness of the V inch. The per cent deflection at 30 bend is [5 material tested, it is not a true modulus of elas ticity in the sense of being independent of the method used in its. determination. The value is not directly comparable with stiffness values determined by other methods, nor is it independent of the span on the instrument used. It can be taken, however, as a relative measure of intrinsic stiffness, and as such furnishes a convenient comparative method for designating the pliability of the interpolyamides.

The products of the invention are not only of particular value in the preparation of wrapping foils and coatings for fabrics, but also are useful in adhesives, safety glass interlayers, impregnating compositions, elastic fabrics, e. g., for foundation garments, and coatings for leather, paper,

rubber, metal and other materials. The products 7 can be formed into useful objects by coating,

compression molding, and injection molding.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is 'to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. A process for forming a. linear interpolyamide having a modulus of stifiness less than 50 l0 lbs./sq. in. which comprises heating at polymerizing temperatures a mixture of reactants consisting essentially of X parts of 6 aminocaproic acid, Y parts of hexamethylenediammonium sebacate, Z parts of hexamethylenediammonium adipate, and T parts of a mixture of hexamethylenediammoni'um suberate and hexamethylenediammonium azelate in approximately 15:85-30:70 proportions, where X++2+T=l00 and the minimum value of the values for X, Y, Z and T being positive, at least three of them being not less than 5, and the values of X, Y, Z and T, being not in excess of 85.

2. An interpolyamide formed in accordance with the process of claim 1.

.3. A process for iorming a linear interpolyamide having a modulus of stiffness less than 50x10 lbs/sq. in. and being soluble to the extent of at least 15% in an 80:20 mixture by volume of ethanol and water at 50 to 75 C., which process comprises heating at polymerizing temperatures a mixture of reactants consisting essentially of X parts of S-aminocaproic acid, Y parts of hexamethylenediammonium sebaeate, Z parts of hexamethylenediammonium adipate, and T parts of a mixtune of hexamethylenediammonium suberate and hexamethylenediammonium azelate in approximately 15:85-30:70 proportions, where X+Y+Z+T=100 and the minimum value of the values for X, Y, Z and T being positive, at least three of them being not less than 5 and the values of X, Y, Z and T, respectively, being not in excess of 85.

4. An interpolyamide formed in accordance with the process of claim 3.

5. A process for forming pliable, 80:20 ethanol-water soluble interpolyamides, which comprises heating at 200-300" C. a mixture of reactants consisting essentially of 20 to 60% of 6- aminocaproic acid and not less than 10% each of at least two of the following polyamide-forming compositions: hexamethylenediammonium adipate, hexamethylenediammonium sebacate, and a mixture of hexamethylenediammonium suberate and hexamethylenediammonium azelate in approximately 15:85-30:70 proportions.

6. An interpolyamide formed in accordance with the process of claim 5.

7. A linear interpolyamide having a modulus of stiifness less than 50 10 lb./sq. in., a melting point of at least 140 C., and being soluble to the extent of 15% in an 80:20 mixture of ethanol and water at 50 to 75 C., the said interpolyamide consisting essentially of the reaction product of approximately 30 to 45% 6-aminocaproic acid, 10 to 50% hexamethylenediammonium adipate, and 10 to 45% hexamethylenediammonium sebacate.

8. An interpolyamide consisting essentially of the reaction product of approximately 30 parts of caprolactam, 40 parts of hexamethylenediammonium adipate, and 30 parts of hexamethylenediammonium sebacate.

MERLIN MARTIN BRUBAKER. WILLIAM E. HANFORD. RICHARD H. WILEY. 

